Sweden is the only country that accepted "asylum seekers" without extensive background check (to verify they actually are asylum seekers) and granted them permanent residency - which makes them legally immune to deportation.
These two facts make those people feel "safe" to commit high crimes.
It is both in this article and many others, it's not like this is a secret.
There are migrants from the same countries that integrated well. The problem is mostly with the "asylum seekers" who never wanted to integrate.